Abstract: Anti adversity characters of X. citri such as extracellular secretions, activity of extracellular protease, ultrastructural changes of the bacterial cells scanning by the TEM and antagonistic dynamics of extracellular products to bactericide amicarthiazol were determined. The results showed that extracellular secretions of X. citri had certain abilities to regulate the interaction between the bacterium and amicarthiazol. Extracellular polysaccharide (EPS), extracellular products and activity of extracellular proteinase of X. citri were increased when treated with 10 μg/mL less of amicarthiazol than in the untreatment, meanwhile, the amount of extracellular protein was decreased. Extracellular products could antagonize the inhibition of amicarthiazol to the growth of X. citri , and give strong protections for the cell to avoid contacting with amicarthiazol, ultrastructure of the cell of X. citri inhibited by amicarthiazol showed to change with concentration of protoplasm. It was concluded that the bacterium of X. citri embraced with the physiological anti-adversity characters under bactericidal selection by amicarthiazol.